The present invention generally relates to endless belt conveyors. More specifically, the present invention relates to an endless belt conveyor having a modular frame, an improved tension and tracking mechanism and a center drive construction that increases the ease with which the conveyor belt can be removed and replaced.
Known constructions of an endless belt conveyor typically includes a frame assembly, a pair of head plates located at each end of the frame assembly, a spindle extending between each pair of head plates, and a conveyor belt engaged between the spindles. One of the spindles is drivingly interconnected with a motor for rotating the spindle to impart movement to the endless conveyor belt. The drive motor can be positioned at either end of the conveyor assembly, or can be center mounted depending upon space constraints.
The head plates utilized in known conveyor constructions are movably mounted to the frame assembly so as to provide selective adjustment of the position of the spindles for providing proper belt tensioning and tracking. One such construction is illustrated in Dorner et al. U.S. Pat. No. 5,174,435, the disclosure of which is incorporated herein by reference.
In the Dorner et al. '435 patent, the conveyor frame is a ladder-type construction consisting of a pair of side frame members interconnected via a series of transversely extending cross members, each of which is connected at its ends to the side frame member. The top of the conveyor is formed by a single, continuous bed plate that is mounted on the cross members and supports the upper run of the endless conveyor belt. T-shaped slots are formed in the side frame members and each head plate is movably mounted to one of the side frame members by means of a T-nut slidably received within the T-shaped slot. A rack and pinion subassembly is mounted adjacent each end of the frame assembly for selectively moving the head plates outward and inward relative to the frame assembly. A cam-type tracking mechanism is interconnected with the rack and pinion subassembly and provides adjustability in the angle of the spindle relative to the conveyor frame for providing proper belt tracking.
Although the conveyor illustrated in the '435 patent is able to adjust belt tension and provide for belt tracking, the cam-type tracking mechanism is interrelated with the tensioning system such that if the belt needs to be retensioned, the belt tracking mechanism is released and needs to be subsequently readjusted. This drawback requires additional set-up time each time the belt needs to be retensioned, which is a clear drawback in the conveyor system.
Another conveyor construction is illustrated in the Hosch et al. U.S. Pat. No. 6,109,427, the disclosure of which is incorporated herein by reference. In the Hosch et al. '427 patent, the top wall of the conveyor includes a central groove that receives a corresponding center rib on the inner surface of the conveyor belt. The interaction between groove and belt provides tracking for the conveyor belt over its continuous length. However, in this configuration, the top plate of the conveyor frame is a single component that must be specifically sized for the conveyor. Thus, the conveyor widths are limited due to the top plate configuration.
The Hosch et al. '427 patent further teaches a rack and pinion subassembly used to provide tensioning for the conveyor belt. The rack and pinion subassembly includes a locking handle that secures the location of the head plate once proper belt tension has been achieved. While this type of construction has been found to be highly satisfactory, it suffers several drawbacks, including the inability to provide belt tracking and the requirement of a conveyor belt having a center rib that is received within the groove formed in the top plate.
Typically, the endless belt of a conveyor is driven either by an end drive unit positioned to drive a spindle located at either end of the conveyor frame or a center drive unit positioned along the length of the conveyor frame and mounted beneath the conveyor frame. In a center drive unit, the continuous belt is wound through a series of rollers, including a drive roller and a tensioning roller, to impart the required motive force to the conveyor belt. One such center drive unit is illustrated in Ewert U.S. Pat. No. 5,203,447, the disclosure of which is incorporated herein by reference. As can be understood in the Ewert '447 patent, the endless belt is entrained around six separate rollers positioned in a tortured path beneath the conveyor frame. The tortured path increases the driving traction on the belt due to the degree of wrap of the belt around the drive spindle and other drive members.
Although the center drive unit illustrated in the '447 patent is efficient for driving the conveyor belt, threading the conveyor belt through the center drive unit is a tedious and time-consuming task. Further, the multiple spindles require additional parts and manufacturing costs to produce.
Therefore, it is an object of the present invention to provide an endless belt conveyor construction that replaces prior frame construction with a modular top platform that lends itself to increased flexibility in manufacturing conveyors of various lengths and widths. It is a further object of the present invention to provide a conveyor frame construction in which the various components can be incorporated in a low profile arrangement without sacrificing strength of the conveyor frame while maintaining optimal belt tensioning and tracking capabilities. A still further object of the invention is to provide a conveyor construction that includes a separate subassembly for rack and pinion type belt tensioning and the belt tracking that allows the belt tensioning to be adjusted without affecting the belt tracking. A still further object of the invention is to provide a conveyor construction having a tracking mechanism that can be adjusted through the head plates of the conveyor to provide proper alignment for the belt. A still further object of the present invention is to provide a conveyor construction that includes a center drive construction that minimizes the number of components and provides a compact design that can be easily threaded with the conveyor belt. Yet a further object of the invention is to provide a conveyor construction having a transfer tail including a stiffener bar that provides the required strength for increased width conveyors while maintaining a small diameter roller. It is yet a further object of the invention to provide for tensioning mechanisms and tracking mechanisms on both end of the conveyor for long belt lengths.